The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Various holding systems are used in manufacturing to hold and/or move objects between locations. Example holding systems are gripper systems and work holding systems or systems that include clamps. Gripper systems are typically used for gripping and/or moving objects between locations. A gripping procedure may include four steps. During a first step, a gripper is closed to grip an object at a first location. During a second step, an external device (or actuator) moves the gripper from the first location to a second location. During a third step, the object is released from the gripper at the second location. During a fourth step, the external device moves the gripper back to the first location to pick up another object.
Work holding systems typically include one or more clamps that are actuated to hold a part. Each clamp may have, for example a hold state and a release state. During the hold state the clamp is actuated to and held in a part holding position. This prevents the part from moving relative to a fixture. During the release state the clamp is actuated to a backoff (or non-holding) position. This allows the part to be removed from the fixture.
Holding systems may be pneumatic-based or electric-based. The pneumatic-based holding systems include a pneumatic circuit. The pneumatic circuit may include a body and pneumatically actuated valves. The valves are opened and closed to adjust a pressure within a cylinder of the body. A piston is translated within the cylinder based on the pressure in the cylinder. Movement of the piston causes holding element(s) (e.g., gripper fingers or a clamp arm) to hold or release an object. In a gripper implementation, the gripper fingers may be in a closed (gripping) state or an open (release) state. In a clamp implementation, the clamp arm may be in a hold state or a release state. Sensors may be used to detect the state of the holding elements by monitoring position of the piston within the cylinder and/or by directly detecting position of the holding elements.
As a first example, the piston may include magnets, which may be detected via sensors externally mounted on the body. The body may include a groove that extends parallel to the direction of motion of the piston. Magneto-resistive sensors may be mounted on the body over the groove and detect movement of the magnets (i.e. movement of the piston). These sensors may be used to generate, for example, OPEN and CLOSE signals or HOLD and RELEASE signals for automation control. The signals indicate whether the holding elements are in the open, closed, hold and/or release states. As another example, externally mounted inductive sensors may be used to sense holding element movement (e.g., gripper jaw and/or finger movement).
Use of the externally mounted sensors has associated disadvantages. In addition to cost of the sensors and associated cables, the cables can degrade due to, for example, iterative cycling through a gripper procedure. Since a gripper is iteratively moved between locations, certain points on the cables can wear out and thus prevent use of the gripper. In addition, manual adjustments may be needed to swap out sensors on a holding system to accommodate objects of different size. Each object may have a respective set of associated sensors.
Electric-based holding systems may include one or more electric motors mounted on a body. The electric motor(s) are used to actuate holding elements. Sensors may be mounted on the body to detect state of the holding device. Similar issues can arise with these sensors as with the sensors of the pneumatic-based holding systems.
In addition, electric current supplied to the electric motor(s) may need to be maintained or adjusted in order to maintain a desired pressure on an object when holding elements are in a closed or hold state. A typical stepper motor may need to remain on (drawing full power) regardless of the location or movement of the holding elements. This can result in the electric motors being operated at increased temperatures for extended periods of time, which can limit maximum output torque levels of the electric motors and/or degrade and reduce operating life of components of the electric motors. Also, as current is maintained, power consumption is increased.